[s-cars] soft brake pedal

[Jerry Scott]

Nicholas
 Check your rotor thicknesses.  You may be under the minimum thickness,
which would cause the extra pedal travel.  The rotors have a minimum
thickness stamped on the outside of each part.  If I recall correctly the
fronts are somewhere around 0.95 in..
Jerry

-----Original Message-----
From: s-car-list-bounces at audifans.com
[mailto:s-car-list-bounces at audifans.com] On Behalf Of Tom Green
Sent: Monday, December 19, 2011 7:36 PM
To: s-car list; Nicholas
Subject: Re: [s-cars] soft brake pedal

You are definitely barking up the wrong tree if you think you are going to
remove the brake booster and shake it to check for loose parts.  The first
link shows the hydraulic brake booster in the UrS4.
The second link has a photo of a vacuum brake booster similar to that in the
Quantum Syncro.  I suggest visiting quattroworld.com for the
UrS4/UrS6/S2/RS2 forum for the FAQ at the top of the forum page.  There
should be sufficient information there to get you going and some known good
suppliers for parts.  Hopefully you won't need that expensive booster but
can probably find a used or even rebuilt  part.

The most common failure for the booster is for it to leak hyd pressure past
internal seals back to the reservoir, which will bleed off pressure in the
system after shutdown and cause the pump to not be able to keep up with
demand during operation.  You can remove the return line from the servo with
the engine off but pressure still in the system to see if it leaks pressure.
If the fluid is dirty, it is usually dark from hose bits eroded over time.
A fluid flush and filter cleaning may disloge some bits that are obstructing
proper valve operation or restricting fluid flow and pressure.  A magnefine
filter in the return line can help keep the system clean.


On Monday December 19, 2011, at 10:57 AM, Nicholas <applen at gmail.com>
wrote:

> So now my brake warning light hardly ever comes on (not sure what to 
> make of that) and bleeding the brakes didn't seem to get rid of my 
> pedal-travel issue. And I'd be surprised if that had anything to do 
> with the intermittent warning light.
>
> On the syncronized forum (I've got a Quantum Syncro Wagon too), 
> someone just mentioned that they are having the same issue and 
> replaced pretty much everything in the brake system before replacing 
> the brake booster. Turns out their booster had corroded on the inside 
> and very little was left of the diaphragm.
>
> So, could I just have a worn-out brake booster? I plan on pulling mine 
> and shaking it so see if it feel like anything is rotten or loose in 
> there (a preliminary test for sure).
>
> Searching for possible replacements I found a wide, wide range of 
> prices and images of what the booster actually is:
>
> http://www.partsgeek.com/ymm/1992/audi/s4.html?category=brake&part=bra
> ke_booster
>
> http://www.theautopartsshop.com/power-brake-booster/cd532671.html
>
> ...which one is (more) right?
>
> Or, am I barking up the wrong tree here?
>
> Cheers,
> -Nick

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